The topic of this thesis is environmental protection by criminal law with a focus on criminal offenses against environmental activists. After the introductory historical context, there is a section with the general characteristics of environmental law, the scientific and theoretical basis for the development of environmental law and the definition of criminal protection of environment. The paper then presents the anatomy and basic characteristics of environmental criminal offenses, what represent the object of these criminal offenses, the conditions for illegality, and the characteristics of the act, guilt and punishable consequences. This is followed by a section on perpetrators and the basis of their responsibility. The paper discusses the legal framework that forms the legal basis for criminal prosecution of environmental crimes. In the Croatian criminal law system, the most important legal source is the Criminal Code, and there are other direct and indirect sources of criminal law provisions. The following is the protection of the environment by criminal law de lege ferenda with regard to Directive (EU)2024/1203 and scientific assumptions of future development. Two chapters refer to the institutions of the European Union whose purpose is to detect and prosecute cross-border criminal offenses, among which criminal offenses with an ecological connotation have a significant share. Then, statistical data on environmental crimes in Croatia from 2009 to 2024 will be analyzed and the limiting factors in the process of achieving criminal environmental protection will be determined. The second part will address the topic of criminal offenses against environmental activists. We will outline the Rainbow Warrior case and then provide a concrete insight into the dangers faced by environmental activists.